Resumen
The wastewater treatment plant of Wathlingen, Germany, has a design capacity of 20,500 p.e. Since 2000, the sewage sludge has been treated in four reed beds with an area of 3000 m2 each. During this time, three of the four polders were emptied once and put into operation again, which has allowed for an evaluation of complete operation cycles from startup to sludge removal. This paper comprises data on polder construction and operating results as well as an economic evaluation of construction, operation, and sludge disposal costs. Results show that sludge DS mass may be reduced by at least 23% and at most 52%. Water content was reduced, but the DS concentration of the product excavated was not higher than around 20% DS. Operation experiences proved that the system is very user-friendly and requiring limited maintenance and control work. To make the best use of this technique, it is recommended a separate area for additional storage and dewatering is provided after the sludge from the polders is removed. This allows for the possibility for the operators to determine the appropriate time and conditions for final disposal.